In many factory settings, and in particular, the semiconductor device factory, material handling systems convey carriers, each containing a predetermined quantity of material known as a “lot,” between stockers, which are carrier storage machines, and process machines which process the lots (hereinafter, a singular reference to “lot” may also include the “carrier” on which it is transported).
FIG. 1 is a diagram schematically showing an exemplary floor plan of a factory for manufacturing semiconductor devices, and FIG. 2 is a diagram schematically showing a conveying control system 50. The conveying of an individual lot 10 between multiple stockers 41,42,43 and between a stocker 41,42,43 and a process machine 31 is conducted by means of a conveyor 25 controlled by the conveying control system 50.
By way of example, FIG. 1 illustrates a view of a process line 20, including a process machine 31 and three stockers 41,42,43. The conveyor 25 can take many forms, commonly being an elevated railway. The receiving and issuing of the lot 10 to and from the process machine 31 and the stockers 41,42,43 along the conveyor 25 is conducted by, for example, a lifting trolley.
A conventional system for controlling the conveyance of the lots 10 will be described with reference to FIGS. 1 and 2. Referring now to FIG. 2, the conveying control system 50 comprises a user interface (“UI”) 52, an execution control system (“ECS”) 54, and a material control system (“MCS”) 56, interconnected with a communication network 58. The ECS 54 comprises a host computer 53 comprising a predefined static flat file that contains a map of a particular lot 10 to a predetermined stocker 41,42,43. A user, such as a manufacturing technician, interacts with the UI 52 to implement a command to the ECS 54. The ECS 54 communicates the command to the MCS 56 for implementation. The communication may be conveyed directly or indirectly.
The MCS 56 includes a carrying host computer 57 that is adapted to accept commands from the ECS 54 to convey a lot 10, and to receive and transmit necessary control data, also referred to as a conveying pattern, to control the conveyor 25 along a conveying path for the conveyance of the lot 10 from, for example, a process machine 31 to one of the stockers 41,42,43. The MCS 56 communicates to the ECS 54 via a network 58 that the command was executed. The ECS 54 updates the lot map and communicates to the UI 52 that the MCS 56 has delivered the lot 10 to one of the stockers 41,42,43, notifying the user.
The static flat file within the host computer 53 does not contain and does not receive state data regarding the status of the stockers 41,42,43, such as whether stockers 41,42,43 are operating and have capacity to store additional lots 10. Further, the static flat file does not provide for the reception of utilization information that would provide for utility status across multiple potentially available stockers 41,42,43 on the same factory floor.
The methodology of the static flat file within the host computer 53 is to store the lot 10 in the best known stocker 41,42,43 location at the time the lot has finished being processed at a previous operation. However, the chosen stocker location is not always ideal for a particular process machine 31 used next in the process. Also multiple process machines 31 that provide the same process operation may be physically located in several different places on the factory floor with varying distances from the stockers 41,42,43. Another problematic factor is the need to convey and redistribute lots 10 between stockers 41,42,43 to alleviate those that are near capacity limits.
These issues result in less than optimal efficiencies, including long delivery times of the lots to a process machine 31, resulting from retrieving lots 10 stored in nonoptimal locations. Nonoptimal locations include, among others, those locations where the stockers 41,42,43 are not in close proximity to the process machine 31 which is about to process the lot. Long material delivery times contribute to process machine idle time, as the process machine 31 is waiting for the material delivery. This in turn translates to longer process cycle times. Furthermore, delivery delay at one process machine 31 also impacts downstream process machine utilization. Consequently, long material delivery times cause significant overall throughput delays in semiconductor manufacturing.